TireFitLab

275/45 R21

What size is 275/45 R21?

275/45 R21 has an overall diameter of about 30.74 in, a section width of 10.83 in and a sidewall height of 4.87 in. It turns roughly 656 times per mile. Below are the exact figures plus plus/minus sizes that stay within the selected diameter tolerance.

Geometric comparison

265/70 R16 stays within the configured tolerance for 275/45 R21: -0.4% diameter and -0.4% speedometer effect.

Geometric comparison
Metric This size: 275/45 R21 Alternative: 265/70 R16 Difference Verdict
Overall diameter 30.74 in 30.61 in -0.4% Within tolerance
Section width 10.83 in 10.43 in -0.39 in Computed difference
Sidewall height 4.87 in 7.30 in +2.43 in Computed difference
Circumference 96.59 in 96.15 in -0.4% Within tolerance
Speedo 0.0% -0.4% -0.4% Within tolerance

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What this geometry means

275/45 R21 has a mid-range sidewall proportion. The marking combines nominal section width 10.83 in, sidewall ratio 45% and rim diameter 21 inches. One sidewall is 4.87 in; both sidewalls make up 32% of the 30.74 in overall diameter, while the rim makes up 68%.

At the nominal 96.59 in circumference, 1,000 rotations cover 2.45 km (1.52 mi); the inverse rates are 408/km and 656/mi.

Section-width mix versus 275/45 R21: 10 narrower, 1 equal-width and 1 wider entries.

The closest diameter entry is 265/70 R16 at -0.4%. Relative to 275/45 R21, it changes nominal section width by -0.39 in, each sidewall by +2.43 in and radius by -0.07 in.

Curated alternatives: 12 sizes, spanning -1.3% to +0.8% in nominal diameter versus 275/45 R21.

Width endpoints in that set are 245/65 R18 (-1.18 in) and 285/40 R22 (+0.39 in) relative to 275/45 R21.

This is a nominal geometry comparison only. Vehicle clearance, wheel width and offset, load and speed ratings, and manufacturer approval still require separate checks.

Specification

Specification
Overall diameter 30.74 in
Section width 10.83 in
Sidewall height 4.87 in
Circumference 96.59 in
Revolutions 408 /km · 656 /mi

In-tolerance sizes

Alternative sizes that stay within the selected diameter tolerance:

In-tolerance sizes
Size Diameter Speedo Verdict
265/70 R16 -0.4% -0.4% ✓ OK
275/55 R19 +0.5% +0.5% ✓ OK
265/65 R17 -0.6% -0.6% ✓ OK
245/65 R18 -0.7% -0.7% ✓ OK
265/60 R18 -0.7% -0.7% ✓ OK
285/40 R22 +0.8% +0.8% ✓ OK
245/70 R17 -0.8% -0.8% ✓ OK
31x10.50 R15 +0.8% +0.8% ✓ OK
31x10.50 R16 +0.8% +0.8% ✓ OK
265/50 R20 -1.0% -1.0% ✓ OK
265/45 R21 -1.2% -1.2% ✓ OK
265/40 R22 -1.3% -1.3% ✓ OK

Compare sizes

Looks valid
Looks valid
Units
Not recommendedWithin tolerance · Diameter -0.4% (-0.14 in) · US (~3%)
  • Not recommended · This rating covers tire geometry only, not vehicle compatibility.
  • Diameter -0.4% · Ride-height change -0.07 in.
  • Speedometer reads high · 60 mph → 59.7 mph.
  • Sidewall +2.43 in · Width -0.39 in.
Diameter-0.4%-0.14 in
Speedo @ 60-0.4%60 mph → 59.7 mph
Sidewall+2.43 inWidth -0.39 in
Ride-height change-0.07 inDiameter ÷ 2
How this result is calculated

Computed from nominal tire-size geometry: diameter, circumference and speedometer error. It does not check vehicle placard approval, load/speed rating, rim-width range, wheel-arch, suspension or brake clearance.

Methodology

Before fitting

  • Check the vehicle placard and owner’s manual first.
  • Match or exceed the required load index and speed rating.
  • Confirm rim-width range, bolt pattern, hub bore, offset and fasteners.
  • Inspect wheel-arch, suspension and brake clearance under real vehicle load.
  • Check TPMS, cold pressure and local roadworthiness rules.
Diameter
30.74 in 30.61 in-0.14 in
Sidewall
4.87 in 7.30 in+2.43 in
Width
10.83 in 10.43 in-0.39 in
Circumference
96.59 in 96.15 in-0.4%
Revs / mile
656 659
Speedo @ 60
60 mph 59.7 mph-0.4%
Ride-height change
0.00 in -0.07 in
True distance per 100 indicated
100 mi 99.6 mi-0.4%
Δ⌀ -0.14 inΔ↔ -0.39 in
  • Current — 275/45 R21
  • New — 265/70 R16
  • Grounded to the road: the axle rises -0.07 in.

Result report

275/45 R21 265/70 R16 · Not recommended · Within tolerance

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Geometric estimate. Always verify physical clearance (arches, suspension, brakes) before fitting.

In-tolerance alternative sizes

In-tolerance alternative sizes
SizeDiameterSpeedo @ 100Use this
OE 275/45R21+0.0%+0.0%

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Last reviewed: 2026-07-22

Technical check
2026-07-22
Content updated
2026-07-22
What changed
  • Added a localized engine-derived geometry signature and matching Markdown narrative.
Methodology